Array speaker system

ABSTRACT

An array speaker system is constituted by a plurality of speaker units, which are equipped with weighting means respectively and to which weight coefficients based on a Bessel function are imparted. An input signal is transmitted through an all-pass filter whose phase rotates by 180° in high-frequency ranges and is then supplied to those of the speaker units whose weight coefficients have negative values. Thus, a signal of an inverse phase is output with respect to low-frequency ranges; hence, it is possible to avoid the deterioration of audio emission characteristics, and it is possible to avoid the occurrence of beams and comb shapes in audio emission characteristics with respect to signals of high-frequency ranges.

TECHNICAL FIELD

This invention relates to array speaker systems in which a plurality ofspeaker units are arrayed in a one-dimensional manner or atwo-dimensional manner.

BACKGROUND ART

Conventionally, array speaker systems in which a plurality of speakersare regularly arranged so as to reproduce and output sounds are known.In these array speaker systems, as a form of trouble due to the use ofplural speakers, there occurs a phenomenon in which as reproduced audiofrequencies become higher, so-called beams and comb shapes (i.e., soundsare spread in a comb-shape manner) emerge in audio emissioncharacteristics, which vary in response to frequencies and which make itdifficult to realize audition of high-frequency sound outside of anaudio emission center position, or in which frequency characteristicsgreatly vary in response to listening positions.

FIGS. 13A to 13E show simulation results regarding audio emissioncharacteristics when fifteen speaker units are vertically and linearlydisposed with 2.5 cm distances therebetween so that they each emit soundof the same phase. That is, FIGS. 13A to 13E show audio emissioncharacteristics measured in horizontal cross-sectional planes andvertical cross-sectional planes when audio frequencies of 500 Hz, 1000Hz, 10 kHz, and 15 kHz are generated with prescribed speaker setuppositions as well as audio emission characteristics (i.e., soundpressure distribution) in a projection plane that is 2 m distant fromthe front surface of the speaker system. Herein, they show that soundpressure becomes higher in white areas compared with black areas.

As shown in the aforementioned drawings, beams and comb shapesapparently occur in audio emission characteristics with respect to audiofrequencies of several kilo Hz or higher.

In order to avoid the occurrence of this phenomenon, a Bessel arraymethod in which by imparting weights using a string of coefficientsbased on a first-order Bessel function to a string of regularly arrangedspeakers, audio emission characteristics are made to be spherical isknown. For example, Japanese Examined Patent Application Publication No.HO 1-25480 discloses a simplified Bessel array.

FIG. 14 is a circuit diagram showing essential parts of an array speakersystem adopting a Bessel array. The array speaker system shown in FIG.14 has fifteen speaker units, wherein reference numerals 11-1 to 11-15designate fifteen speaker units that are linearly disposed with aprescribed distance d (e.g., d=2.5 cm) therebetween; and referencenumerals 12-1 to 12-15 designate weighting means for imparting weightcoefficients C1 to C15 to signals respectively supplied to thecorresponding speaker units 11-1 to 11-15. Normally, power amplifiersare inserted between the weighting means 12-1 to 12-15 and thecorresponding speaker units 11-1 to 11-15, but the present specificationomits the illustration thereof. As the weighting means 12-1 to 12-15, itis possible to use amplifiers having gains corresponding to weightcoefficients.

Herein, the weight coefficients C1 to C15 are each calculated based onthe first-order Bessel function that is defined by the followingequation.${J_{n}(x)} = {\left( \frac{x}{2} \right)^{n}{\sum\limits_{k = 0}^{\infty}\quad\frac{\left( {- 1} \right)^{k}\left( {x/2} \right)^{2k}}{{k!}{\Gamma\left( {n + k + 1} \right)}}}}$

In this example in which fifteen speaker units are used, values ofJ⁻⁷(x) to J₇(x) according to the aforementioned equation are used. Whenx=6.0, it is possible to produce weight coefficients C1 to C15 impartedto the fifteen speakers as follows:C1=J ⁻⁷(6)=−0.1296C2=J ⁻⁶(6)=0.2458C3=J ⁻⁵(6)=−0.3621C4=J ⁻⁴(6)=0.3576C5=J ⁻³(6)=−0.1148C6=J ⁻²(6)=−0.2429C7=J ⁻¹(6)=0.2767C8=J ₀(6)=0.1506C9=J ₁(6)=−0.2767C10=J ₂(6)=−0.2429C11=J ₃(6)=0.1148C12=J ₄(6)=0.3576C13=J ₅(6)=0.3621C14=J ₆(6)=0.2458C15=J ₇(6)=0.1296

FIGS. 15A to 15E show simulation results regarding audio emissioncharacteristics measured when the speaker units 11-1 to 11-15, to whichweight coefficients C1 to C15 based on the first-order Bessel functionare imparted, are driven, wherein they show audio emissioncharacteristics measured in horizontal cross-sectional planes andvertical cross-sectional planes when audio frequencies of 500 Hz, 1000Hz, 5000 Hz, 10 kHz, and 15 kHz are generated with prescribed speakersetup positions as well as audio emission characteristics in aprojection plane that is 2 m distant from the front surface of thespeaker system.

Compared with FIGS. 13A to 13E, FIGS. 15A to 15E show that no beams andno comb shapes occur in audio emission characteristics in the Besselarray; hence, it is possible to realize the aforementioned sphericalaudio emission characteristics. As described above, driving the speakerunits using the weight coefficients based on the Bessel function is aneffective measure for avoiding the occurrence of beams and comb shapesin audio emission characteristics.

However, as the weight coefficients C1 to C15 based on the Besselfunction include negative values, audio emission characteristics in lowfrequency ranges may deteriorate; therefore, it is difficult toreproduce low-frequency sound. In particular, such a phenomenon brings abad result in array speaker systems in which plural speaker units areinstalled in common enclosures or common enclosures of the bass-reflextype.

In consideration of the aforementioned circumstances, it is an object ofthe present invention to provide an array speaker system in which in abroad range of frequencies ranging from low frequencies to highfrequencies, it is possible to avoid the occurrence of beams and combshapes in audio emission characteristics and to efficiently realizeaudio emission.

DISCLOSURE OF THE INVENTION

An array speaker system of this invention is constituted by arraying aplurality of speaker units, wherein all speaker units are driven withthe same phase in response to signals of low-frequency ranges, while thespeaker units are separately driven with weight coefficients based on aBessel function in response to signals of high-frequency ranges.

Alternatively, it is possible to drive all speaker units with the samephase and with the same gain in response to-signals of low-frequencyranges.

In addition, all-pass filters that are set up to realize phase rotationof 180° in high-frequency ranges are arranged, so that speaker unitswhose weight coefficients based on the Bessel function have negativevalues are driven with absolute values of weight coefficients, which areimparted to signals supplied thereto by way of the all-pass filters,while other speaker units whose weight coefficients based on the Besselfunction do not have negative values are directly driven with the weightcoefficients thereof without the intervention of the all-pass filters.

Furthermore, in an array speaker system of this invention, there areprovided all-pass filters that are set up to realize phase rotation of180° in high-frequency ranges, means that are respectively connected tospeaker units whose weight coefficients based on the Bessel functionhave negative values so as to impart gain characteristics correspondingto absolute values of weight coefficients to signal components ofhigh-frequency ranges within signals input thereto by way of theall-pass filters, and means that are respectively connected to speakerunits whose weight coefficients based on the Bessel function do not havenegative values so as to impart gain characteristics corresponding toweight coefficients to signal components of high-frequency ranges.

The aforementioned all-pass filters can be set up in such a way that thephase rotation thereof is set to 90° with respect to frequencies inproximity to frequencies corresponding to wavelengths corresponding towidths of speaker units.

Furthermore, in an array speaker system of this invention, there areprovided filter means for dividing input signals into signal componentsof low-frequency ranges and signal components of high-frequency ranges,weighting means that are respectively connected to speaker units so asto impart weight coefficients based on the Bessel function to signalcomponents of high-frequency ranges, and addition means that arerespectively connected to speaker units so as to add signal componentsof low-frequency ranges to signal components of high-frequency ranges,to which weight coefficients based on the Bessel function are impartedby the weighting means, thus outputting addition results to the speakerunits.

Incidentally, in the array speaker system of this invention, a pluralityof speaker units are installed in a common enclosure or a commonenclosure of a bass-reflex type, for example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram showing essential parts of an array speakersystem in accordance with a first embodiment of this invention;

FIG. 2A shows an example of the constitution of an all-pass filter shownin FIG. 1;

FIG. 2B shows phase characteristics of the all-pass filter;

FIG. 3A shows audio emission characteristics measured upon generation ofan audio frequency of 500 Hz in the array speaker system of the firstembodiment;

FIG. 3B shows audio emission characteristics measured upon generation ofan audio frequency of 1000 Hz in the array speaker system of the firstembodiment;

FIG. 3C shows audio emission characteristics measured upon generation ofan audio frequency of 5000 Hz in the array speaker system of the firstembodiment;

FIG. 3D shows audio emission characteristics measured upon generation ofan audio frequency of 10 kHz in the array speaker system of the firstembodiment;

FIG. 3E shows audio emission characteristics measured upon generation ofan audio frequency of 15 kHz in the array speaker system of the firstembodiment;

FIG. 4A shows an example of the constitution of an IIR digital all-passfilter;

FIG. 4B shows phase characteristics of the IIR digital all-pass filter;

FIG. 5 is a circuit diagram showing essential parts of an array speakersystem in accordance with a second embodiment of this invention;

FIG. 6A shows an example of the constitution of an amplifier connectedto a prescribed speaker unit;

FIG. 6B shows an example of the constitution of a high-pass filter of ashelving type, which is connected to a prescribed speaker unit;

FIG. 6C shows an example of the constitution of a high-cut filter of ashelving type, which is connected to a prescribed speaker unit;

FIG. 7 show gain characteristics of circuits that are constituted asshown in FIGS. 6A to 6C;

FIG. 8A shows an example of a circuit constitution of a filter connectedto each speaker unit in an array speaker system in accordance with athird embodiment of this invention;

FIG. 8B shows gain characteristics of the filter shown in FIG. 8A;

FIG. 8C shows phase characteristics of the filter shown in FIG. 8A;

FIG. 9A shows another example of the circuit constitution of theaforementioned filter;

FIG. 9B shows gain characteristics of the filter shown in FIG. 9A;

FIG. 9C shows phase characteristics of the filter shown in FIG. 9A;

FIG. 10 is a circuit diagram showing essential parts of the arrayspeaker system in accordance with the third embodiment of thisinvention;

FIG. 11A shows audio emission characteristics measured upon generationof an audio frequency of 900 Hz when the gain of each speaker unit isset to “1”;

FIG. 11B shows audio emission characteristics measured upon generationof an audio frequency of 1000 Hz when the gain of each speaker unit isset to “1”;

FIG. 11C shows audio emission characteristics measured upon generationof an audio frequency of 1200 Hz when the gain of each speaker unit isset to “1”;

FIG. 11D shows audio emission characteristics measured upon generationof an audio frequency of 1500 Hz when the gain of each speaker unit isset to “1”;

FIG. 12 is a circuit diagram showing essential parts of an array speakersystem in accordance with a fourth embodiment of this invention;

FIG. 13A shows audio emission characteristics measured upon generationof an audio frequency of 500 Hz in the conventional array speakersystem;

FIG. 13B shows audio emission characteristics measured upon generationof an audio frequency of 1000 Hz in the conventional array speakersystem;

FIG. 13C shows audio emission characteristics measured upon generationof an audio frequency of 5000 Hz in the conventional array speakersystem;

FIG. 13D shows audio emission characteristics measured upon generationof an audio frequency of 10 kHz in the conventional array speakersystem;

FIG. 13E shows audio emission characteristics measured upon generationof an audio frequency of 15 kHz in the conventional array speakersystem;

FIG. 14 is a circuit diagram showing essential parts of an array speakersystem adopting a Bessel array;

FIG. 15A shows audio emission characteristics measured upon generationof an audio frequency of 500 Hz in the array speaker system adopting theBessel array;

FIG. 15B shows audio emission characteristics measured upon generationof an audio frequency of 1000 Hz in the array speaker system adoptingthe Bessel array;

FIG. 15C shows audio emission characteristics measured upon generationof an audio frequency of 5000 Hz in the array speaker system adoptingthe Bessel array;

FIG. 15D shows audio emission characteristics measured upon generationof an audio frequency of 10 kHz in the array speaker system adopting theBessel array; and

FIG. 15E shows audio emission characteristics measured upon generationof an audio frequency of 15 kHz in the array speaker system adopting theBessel array.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of this invention will be described in detail withreference to the accompanying drawings.

First, a description will be given with respect to the basic principleof an array speaker system of this invention.

As shown in audio emission characteristics shown in FIGS. 13A to 13E,when all speaker units forming the array speaker system emit sounds ofprescribed audio frequencies with the same phase, no beams and no combshapes occur in audio emission characteristics in low-frequency ranges(i.e., frequencies of 1 kHz or lower shown FIGS. 13A and 13B) even whenweighting is not effected using weight coefficients based on the Besselfunction. For this reason, this invention is designed such that inlow-frequency ranges causing no problem due to beams and comb shapes inaudio emission characteristics, the speaker units are each driven withthe positive phase so as to prevent audio emission characteristics fromdeteriorating, while in high-frequency ranges causing beams and combshapes in audio emission characteristics, the speaker units are eachdriven with weight coefficients based on the Bessel function. Thus, in abroad range of frequencies ranging from low-frequency ranges tohigh-frequency ranges, it is possible to efficiently perform soundemission while avoiding the occurrence of beams and comb shapes in audioemission frequencies.

Hereinafter, a description will be given with respect to an arrayspeaker system of this invention in which speaker units are each drivenwith the positive phase in low-frequency ranges and are each driven withweight coefficients based on the Bessel function in high-frequencyranges.

FIG. 1 is a circuit diagram showing essential parts of an array speakersystem in accordance with a first embodiment of this invention. In thepresent embodiment similarly to in the conventional example, the arrayspeaker system is formed using fifteen speaker units, wherein weightcoefficients based on the Bessel function are set similar to theforegoing values of C1 to C15. However, this invention is notnecessarily limited to the aforementioned constitution; hence, thisinvention can be similarly applied to other array speaker systems eachhaving plural speaker units (e.g., five speaker units or more), whereinweight coefficients can be set to prescribed values other than theforegoing values of C1 to C15.

In addition, the present embodiment is designed such that speaker unitsare each driven with the positive phase in low-frequency ranges and areeach driven with weight coefficients based on the Bessel function inhigh-frequency ranges. For this reason, the present embodiment usesall-pass filters whose phases vary by 180° in high-frequency ranges.

In FIG. 1, reference numerals 1-1 to 1-15 designate fifteen speakerunits that are disposed with a prescribed distance d (e.g., d=2.5 cm)therebetween; and reference numerals 2-1 to 2-15 designate weightingmeans for weighting signals, which are supplied to the correspondingspeaker units 1-1 to 1-15, by use of weight coefficients based on theBessel function. They correspond to ones designated by referencenumerals 11-1 to 11-15 and reference numerals 12-1 to 12-15 shown inFIG. 14. However, FIG. 1 differs from FIG. 14 in that weightcoefficients adopted in the weighting means 2-1 to 2-15 are given asabsolute values. That is, in the array speaker system shown in FIG. 14,negative values are set to the weight coefficients C1, C3, C5, C6, C9,and C10, whereas in the array speaker system shown in FIG. 1, theweighting means 2-1, 2-3, 2-5, 2-6, 2-9, and 2-10 adopt weightcoefficients C1′, C3′, C5′, C6′, C9′, and C10′ represented by absolutevalues.

A reference numeral 3 designates an all-pass filter whose amplitudecharacteristics are flat over all frequency ranges and whose phasecharacteristics realize phase rotation of 0° in low-frequency ranges butare reversed by way of variation of 180° in high-frequency ranges.

FIG. 2A shows an example of the constitution of the all-pass filter; andFIG. 2B shows phase characteristics thereof. As shown in FIG. 2B, theall-pass filter 3 has phase characteristics in which the phase rotationis set to 0° in low-frequency ranges, it is gradually increased asfrequency becomes higher, it reaches 90° at approximately 700 Hz, and itis set to 180° in high-frequency ranges that are 10 kHz or above.

In FIG. 1, an input signal applied to a signal input terminal isdirectly supplied to the weighting means 2-2, 2-4, 2-7, 2-8, 2-11, 2-12,2-13, 2-14, and 2-15 whose weight coefficients based on the Besselfunction have positive values, while it is supplied to the otherweighting means 2-1, 2-3, 2-5, 2-6, 2-9, and 2-10 by way of the all-passfilter 3. The input signal being supplied as described above is givenindividual weight coefficients in the weighting means 2-1 to 2-15,outputs of which are then supplied to the speaker units 1-1 to 1-15respectively.

That is, signals to which weight coefficients are applied in thecorresponding weighting means are respectively supplied to the speakerunits 1-2, 1-4, 1-7, 1-8, and 1-11 to 1-15 whose weight coefficientsbased on the Bessel function have positive values. In addition,weighting having the same phase (i.e., the same polarity) as theweighting applied to the speaker units whose weight coefficients basedon the Bessel function have positive values is applied to the speakerunits 1-1, 1-3, 1-5, 1-6, 1-9, and 1-10 whose weight coefficients basedon the Bessel function have negative values with respect tolow-frequency signals on which the all-pass filter 3 effects phaserotation not exceeding 90°. In contrast, with respect to high-frequencysignals on which the all-pass filter 3 effects phase rotation exceeding90°, weighting having the reverse phase (i.e., the reverse polarity) asthe weighting applied to the speaker units whose weight coefficientsbased on the Bessel function have positive values is applied to them.

That is, in high-frequency ranges, negative weight coefficients areapplied to the speaker units whose weight coefficients based on theBessel function have negative values, thus making the weightcoefficients based on the Bessel function operate effectively. Inlow-frequency ranges, signals having the same phase are supplied to thecorresponding speaker units; therefore, it is possible to reproducelow-frequency sound with a sufficient amplitude.

FIGS. 3A to 3E show simulation results of audio emission characteristicsin the present embodiment, and show audio emission characteristicsmeasured in horizontal cross-sectional planes and verticalcross-sectional planes when audio frequencies of 500 Hz, 1000 Hz, 5000Hz, 10 kHz, and 15 kHz are generated with prescribed speaker setuppositions as well as audio emission characteristics in the projectionplane that is 2 m distant from the front surface of the speaker system.

Compared with the foregoing audio emission characteristics shown inFIGS. 13A to 13E, as shown in FIGS. 3A to 3E, it is possible toadequately avoid the occurrence of beams and comb shapes in audioemission characteristics in the present embodiment.

Incidentally, the all-pass filter 3 is not necessarily formed using ananalog filter as shown in FIG. 2A; hence, it can be formed using adigital filter equipped with an A/D converter and a D/A converter beforeand after it.

For instance, suppose that the analog all-pass filter 3 shown in FIG. 2Ahas a transfer function as follows:${H(S)} = \frac{1 - {CRS}}{1 + {CRS}}$

It is subjected to bilinear transform in a Z-axis region by use of thefollowing formula.$S = \frac{2}{T*\frac{\left( {1 - Z^{- 1}} \right)}{1 + Z^{- 1}}}$

Hence, it is transformed as follows:${H(Z)} = \frac{\left( {T - {2{CR}}} \right) + {\left( {T + {2{CR}}} \right)Z^{- 1}}}{\left( {T + {2{CR}}} \right) + {\left( {T - {2{CR}}} \right)Z^{- 1}}}$

In the above, when C=0.047 μF, R=4.7 kΩ, and sampling frequency fs=48Hz, it is represented as follows:${H(Z)} = \frac{{{- 420}*10^{- 1}} + {\left( {460*10^{- 1}} \right)Z^{- 1}}}{{460*10^{- 1}} + {\left( {{- 420}*10^{- 1}} \right)Z^{- 1}}}$

This digital filter can be formed using an IIR (Infinite ImpulseResponse) filter shown in FIG. 4A, which has the phase characteristicsshown in FIG. 4B.

As described above, the speaker units each have different weightcoefficients based on the Bessel function. For example, in the case ofthe weight coefficients C1 to C15 shown in FIG. 14, C3=−0.3621 whoseabsolute value is maximal is increased in gain approximately 3.15 timesmore than C5=−0.1148 whose absolute value is minimal. For this reason,audio conversion efficiency in low-frequency ranges, which do not needweighting using weight coefficients based on the Bessel function, mustbe reduced.

A second embodiment of this invention, which is designed to eliminatethe aforementioned drawback, will be described with reference to FIG. 5,FIGS. 6A to 6C, and FIG. 7.

In the second embodiment, filters that have the same gain with respectto low-frequency ranges and that have gains in response to weightcoefficients based on the Bessel function with respect to high-frequencyranges are used as weighting means. That is, a reference speaker unit isset up; then, flat gain characteristics are applied to the referencespeaker unit. For the other speaker units, the same gain as the gain ofthe reference speaker unit is set with respect to low-frequency ranges;and filters having gain characteristics, which represent ratios ofweight coefficients of the other speaker units, compared with the weightcoefficient of the reference speaker unit, are used as weighting meanswith respect to high-frequency ranges. Incidentally, similarly to in theaforementioned first embodiment, the output of the all-pass filter 3 isdirectly supplied to the speaker units whose weight coefficients basedon the Bessel function have negative values.

In FIG. 5, reference numerals 1-1 to 1-15 designate speaker units;reference numeral 3 designates an all-pass filter; and referencenumerals 4-1 to 4-15 designate circuits for imparting prescribed weightsto speaker units 1-1 to 1-15. In the second embodiment, the speaker unit1-1 (weight coefficient C1′=0.1296) is used as the reference speakerunit. Because of the relationship regarding weight coefficients C15=C1′,the speaker unit 1-15 corresponds to the reference speaker unit.Therefore, amplifiers 4-1 and 4-15 having flat frequency characteristicsare connected to the reference speaker units 1-1 and 1-15 respectively.

As absolute values of weight coefficients applied to the speaker units1-2 to 1-4, 1-6 to 1-10, and 1-12 to 1-14 are greater than the absolutevalue 0.1296 of the weight coefficient applied to the reference speakerunit, high-pass filters 4-2 to 4-4, 4-6 to 4-10, and 4-12 to 4-14, eachof which is a so-called shelving type, are connected to them. Thesehigh-pass filters have flat gain characteristics in low-frequencyranges; and they also have gain characteristics that are increased inresponse to ratios of the weight coefficients applied to thecorresponding speaker units compared with the reference weightcoefficient C1 (C15) with respect to high-frequency ranges.

Both of the weight coefficients applied to the other speaker units 1-5and 1-11 are set to 0.1148, which is lower than the reference weightcoefficient 0.1296. Hence, high-cut filters of the shelving type thathave flat gain characteristics in low-frequency ranges and that alsohave gain characteristics, which are decreased in response to ratios ofthe weight coefficients thereof compared with the reference weightcoefficient C1, are connected to them.

FIG. 6A shows an example of the constitution adapted to theaforementioned amplifiers 4-1 and 4-15. FIG. 6B shows an example of theconstitution adapted to the aforementioned high-pass filters 4-2 to 4-4,4-6 to 4-10, and 4-12 to 4-14. Furthermore, FIG. 6C shows an example ofthe constitution adapted to the aforementioned high-cut filters 4-5 and4-11.

In the circuits shown in FIGS. 6A to 6C, a dc gain (i.e., a gain inlow-frequency ranges) is determined by a ratio (R2/R1) between resistorsR2 and R1. In addition, the same values of the resistors R1 and R2 areused in the circuits designated by reference numerals 4-1 to 4-15.Therefore, the same gain is applied to signals supplied to the speakerunits 1-1 to 1-15 with respect to low-frequency ranges. Specifically,the setup is made such that R1=33 kΩ and R2=47 kΩ; therefore, the dcgain is set to 20 log(47/33)=3.07 dB.

In each of the high-pass filter and high-cut filter shown in FIGS. 6Band 6C, prescribed values are selected for a resistor R3 and a capacitorC respectively in order for the gain in high-frequency ranges to be setin response to the ratio of the absolute value of the correspondingweight coefficient compared with the reference weight coefficient(0.1296).

For example, with respect to the high-pass filter 4-2 having the weightcoefficient C2=0.2458, circuit constants thereof (i.e., R3=36 kΩ, C=3300pF) are determined in order for the gain thereof in high-frequencyranges to be increased by 20 log(0.2458/0.1296)=5.56 dB compared withthe gain of the amplifier 4-1 connected to the reference speaker unit1-1, i.e., it is set to 3.07+5.56=8.63 dB. With respect to the high-passfilter 4-3, circuit constants thereof (i.e., R3=18 kΩ, C=5600 pF) aredetermined in order for the gain thereof in high-frequency ranges to beset to 20 log(0.3621/0.1296)+3.07=12.0 dB. Similarly, with respect tothe high-pass filter 4-4, the gain thereof is set to 20log(0.3576/0.1296)+3.07=11.9 dB, which is approximately identical to thegain of the high-pass filter 4-3; hence, circuit constants thereof(i.e., R3=18 kΩ, C=5600 pF) are similarly set up. Based on similarcalculations, circuit constants of R3=36 kΩ and C=3300 pF are set withrespect to the high-pass filter 4-6; circuit constants of R3=30 kΩ andC=3900 pF are set with respect to the high-pass filter 4-7; circuitconstants of R3=20 kΩ and C=1000 pF are set with respect to thehigh-pass filter 4-8; circuit constants of R3=30 kΩ and C=3900 pF areset with respect to the high-pass filter 4-9; circuit constants of R3=36kΩ and C=3300 pF are set with respect to the high-pass filter 4-10;circuit constants of R3=18 kΩ and C=5600 pF are set with respect to thehigh-pass filter 4-12; circuit constants of R3=18 kΩ and C=5600pF areset with respect to the high-pass filter 4-13; and circuit constants ofR3=36 kΩ and C=3300 pF are set with respect to the high-pass filter4-14.

Furthermore, both of the high-cut filters 4-5 and 4-11 have the sameweight coefficient whose absolute value is 0.1148; hence, circuitconstants thereof (i.e., R3=360 kΩ, C=470 pF) are determined as shown inFIG. 6C in order for the gain thereof in high-frequency ranges to have adifference of 20 log(0.1148/10.1296)=−1.05 dB compared with the gain ofthe amplifier 4-1 connected to the reference speaker unit, i.e., it isset to 3.07−1.05=2.02 dB.

FIG. 7 shows gain characteristics of the aforementioned circuitsdesignated by reference numerals 4-1 to 4-15. As shown in FIG. 7, thecircuits each have the same gain and flat characteristics inlow-frequency ranges, whereas the gains thereof in high-frequency rangesare varied in response the corresponding weight coefficient.

As described above, in the second embodiment, in low-frequency ranges atwhich no problem occurs with regard to beams and comb shapes in audioemission characteristics, signals having the same phase and the samegain are supplied to the speaker units, wherein as frequencies becomehigher, signals given weights based on the Bessel function are suppliedto them. Therefore, in the present embodiment, it is possible to preventthe audio emission efficiency in the low-frequency sound from beingreduced; and it is possible to avoid the occurrence of beams and combshapes in audio emission characteristics.

Incidentally, in the aforementioned embodiment, the speaker unit 1-1 isselected as the reference speaker unit, but this invention is notnecessarily limited by the aforementioned embodiment; hence, it ispossible to arbitrarily select a desired speaker unit as the referencespeaker unit. In addition, it is possible to form the aforementionedhigh-pass filters and high-cut filters by use of digital filters,instead of analog filters.

A third embodiment of this invention, in which similarly to in thesecond embodiment shown in FIG. 5, FIGS. 6A to 6C, and FIG. 7, the samegain is set with respect to low-frequency ranges, and weights based onthe Bessel function are applied with respect to high-frequency ranges,will be described with reference to FIGS. 8A to 8C, FIGS. 9A to 9C, andFIG. 10.

In the third embodiment, a feedback resistor connected between theoutput terminal and inverting input terminal of the operationalamplifier in the all-pass filter 3 shown in FIG. 2 is set to a valuethat differs from values of other resistors, thus applying desiredfrequency characteristics to gains. That is, a filter whose weightcoefficient based on the Bessel function has a negative value isconnected to a certain speaker unit as a weighting circuit, thusomitting the all-pass filter 3 that is provided in common with respectto speaker units whose weight coefficients based on the Bessel functionhave negative values.

FIG. 8A shows an example of the circuit constitution of theaforementioned filter.

Within the aforementioned weight coefficients C1 to C15, the weightcoefficients C3 and C13 whose absolute values (i.e., 0.3621) are maximalare selected as reference coefficients, and are then normalized to “1”.For example, the weight coefficient C5=−0.1148 has an absolute valuethat is represented as 1/3.15(=0.1148/0.3621); hence, the gain appliedto the corresponding speaker unit 1-5 is adjusted to have a differenceof 20 log(1/3.15)=−9.97 dB compared with the gain of the other speakerunit 1-3.

The filter shown in FIG. 8A has a transfer function as follows:${H(S)} = \frac{1 - {{CR}\quad 2S}}{1 - {{CR}\quad 1S}}$

In the above, when circuit constants are set as C=0.1 μF, R1=4.7 kΩ, andR2=1.5 kΩ, it is possible to realize the gain characteristics shown inFIG. 8B and phase characteristics shown in FIG. 8C. That is, it ispossible to provide gain characteristics having a dc gain of 0 dB and again of −9.97 dB in high-frequency ranges as well as phasecharacteristics having phase rotation of 0° in low-frequency ranges andphase rotation of 180° in high-frequency ranges.

Similarly to above, prescribed circuit constants can be determined inresponse to gain characteristics with respect to weight coefficients offilters connected to the other speaker units.

With respect to speaker units whose weight coefficients based on theBessel function have positive values, it is possible to use filtershaving gain characteristics in response to ratios of the weightcoefficients compared with the reference weight coefficient, and thesefilters can be embodied by the circuitry shown in FIG. 9A, for example.

For example, with respect to the filter corresponding to the weightcoefficient C11=0.1148, the left-side circuit portion of the filtershown in FIG. 9A has a transfer function as follows:${H(S)} = \frac{{- 1}*R\quad 2}{\frac{R\quad 1*\left( {1 + {{CR}\quad 3S}} \right)}{1 + {\left( {{{CR}\quad 2} + {{CR}\quad 3}} \right)S}}}$

In the above, when circuit constants are set as R1=4.7 kΩ, R2=4.7 kΩ,R3=2.7 kΩ, and C−0.1 μF, it is possible to realize the gaincharacteristics shown in FIG. 9B and phase characteristics shown in FIG.9C. That is, it is possible to realize gain characteristics having a dcgain of 0 dB in which the gain is reduced to −9.97 dB as the frequencybecomes higher. The phase characteristics shown in FIG. 9C indicate thatthe phase maximally rotates by approximately 30°, and no problem occursdue to such a phase rotation over phase characteristics.

Similarly, prescribed circuit constants can be determined with respectto filters connected to the other speaker units whose weightcoefficients have positive values.

FIG. 10 is a circuit diagram showing the constitution of an arrayspeaker system in accordance with the third embodiment of thisinvention, which is constituted using the filter shown in FIG. 9Ainstead of the filter shown in FIG. 8A. In the third embodiment, weightcoefficients C3 and C13 whose absolute values are maximal within weightcoefficients based on the Bessel function are selected as referenceweight coefficients, and an all-pass filter 5-3 whose phase inverts inhigh-frequency ranges as shown in FIGS. 2A and 2B is connected to thespeaker unit 1-3 whose weight coefficient has a negative value, while anamplifier 5-13 having a gain of 1 is connected to the speaker unit 1-13whose weight coefficient has a positive value (alternatively, theamplifier 5-13 can be left out).

The filter shown in FIG. 8A having a gain in response to the ratiobetween the absolute value of the reference weight coefficient (i.e.,0.3621) and the absolute value of the weight coefficient applied to thecorresponding speaker unit in high-frequency ranges is connected to eachof the speaker units 1-1, 1-5, 1-6, 1-9, and 1-10 whose weightcoefficients have negative values within the other speaker units.

In addition, the filter shown in FIG. 9A having a gain in response tothe ratio between the absolute value of the reference weight coefficientand the weight coefficient applied to the corresponding speaker unit inhigh-frequency ranges is connected to each of the speaker units 1-2,1-4, 1-7, 1-8, 1-11, 1-12, 1-14, and 1-15 whose weight coefficients havepositive values.

As described above, in the third embodiment, the same gain having thesame phase is applied to each of the speaker units with respect tolow-frequency ranges having no problem regarding beams and comb shapesin audio emission characteristics, while weight coefficients based onthe Bessel function are applied to each of them with respect tohigh-frequency ranges. Therefore, it is possible to avoid a degradationof audio emission characteristics in low-frequency sound; and it ispossible to avoid the occurrence of beams and comb shapes in audioemission characteristics. Furthermore, it is possible to omit theall-pass filter, which is connected in common to all speaker units.

The aforementioned embodiment is described and embodied using analogfilters, but it can be embodied using a digital filter shown in FIG. 4Arealizing SZ transform (e.g., bilinear transform). In addition, it ispossible to arbitrarily select the reference speaker unit.

Next, a center frequency (i.e., a frequency causing phase rotation of90°) in the phase rotation of the aforementioned all-pass filter and thefilter shown in FIG. 8A will be described.

For example, in the aforementioned simulation, fifteen speaker units aredisposed with the distance d (=2.5 cm) therebetween, wherein the overallwidth of the speaker unit string is 35 cm (=2.5 cm×14). Simulation isperformed in consideration of the speed of sound, i.e., 340 m/sec, sothat the frequency having a single wavelength corresponding to the widthof the speaker unit string, i.e., 35 cm, is 34000/35=971 Hz.

FIGS. 11A to 11D show simulation results that are produced when all thefifteen speaker units have the same weight of 1. Herein, FIGS. 11A, 11B,11C, and 11D show audio emission characteristics in response to audiofrequencies of 900 Hz, 1000 Hz, 1200 Hz, and 1500 Hz respectively.

FIGS. 11A to 11D show that sound beams may apparently emerge infrequencies higher than the prescribed frequency (approximately, 1000Hz) substantially corresponding to the wavelength having the width ofthe speaker unit string. For this reason, the center frequency (i.e.,the frequency causing phase rotation of 90°) in the phase rotation ofthe all-pass filter or the filter shown in FIG. 8A is set in conformitywith the wavelength having the width of the speaker unit string, so thatweighting effects due to weight coefficients based on the Besselfunction may start to work in frequencies higher than the centerfrequency; thus, it is expected to produce an improved result withregard to audio emission characteristics.

As described above, it is preferable that the center frequency(corresponding to phase rotation of 90°) in the phase rotation of theall-pass filter be set in proximity to the frequency corresponding tothe wavelength of the speaker unit string of the array speaker system.

The aforementioned embodiment is constituted using the all-pass filter(or the filter shown in FIG. 8A), which is formed in an analog ordigital manner, whereas this invention can be embodied using othermeasures.

FIG. 12 shows essential parts of the circuit configuration of an arrayspeaker system in accordance with a fourth embodiment of this invention,which is constituted without using the aforementioned all-pass filter.

Reference numerals 1-1 to 1-15 designate speaker units similar to theforegoing ones; reference numeral 6 designates a low-pass filter forfiltering signal components of low-frequency ranges from input signals;reference numeral 7 designates a high-pass filter for filtering signalcomponents of high-frequency ranges from input signals; referencenumerals 8-1 to 8-15 designate weighting means for imparting weightsusing weight coefficients C1 to C15 based on the Bessel function tosignal components of high-frequency ranges supplied from the high-passfilter 7; and reference numerals 9-1 to 9-15 designate adders, which arearranged in correspondence with the speaker units 1-1 to 1-15respectively and which add signal components of low-frequency ranges (towhich a gain of 1 is applied) provided from the low-pass filter 6 andsignal components of high-frequency ranges, to which the weighting means8-1 to 8-15 impart weights based on the Bessel function, together, thussupplying addition results to the speaker units 1-1 to 1-15respectively. Herein, the same cutoff frequency is set for the low-passfilter 6 and the high-pass filter 7, for example; hence, input signalsare divided into signal components of low-frequency ranges and signalcomponents of high-frequency ranges. Incidentally, the low-pass filter 6and the high-pass filter 7 can be each constituted using an analogfilter or a digital filter.

In the aforementioned fourth embodiment, input signals are divided intosignal components of low-frequency ranges and signal components ofhigh-frequency ranges by use of the frequency corresponding to thewavelength identical to the width of the speaker unit string; thecorresponding speaker units are subjected to weighting using a gain of 1with respect to signal components of low-frequency ranges; they aresubjected to weighting using weight coefficients based on the Besselfunction with respect to signal components of high-frequency ranges; andthereafter, these signals components are added together and output.Thus, similarly to in the foregoing embodiments using the all-passfilters, it is possible to secure a sufficiently high gain inlow-frequency ranges, and it is possible to avoid the occurrence ofbeams and comb shapes in audio emission characteristics with respect tohigh-frequency ranges.

The aforementioned embodiments are each constituted using fifteenspeaker units; however, this invention effectively works in any arrayspeaker system having five speaker units or more. In addition, weightcoefficients based on the Bessel function are not necessarily limited tothe aforementioned values.

As described heretofore, in the array speaker system of this invention,speaker units are each driven with positive phases with respect tolow-frequency ranges; hence, it is possible to prevent audio emissioncharacteristics from deteriorating irrespective of inverse phasecomponents, which occur due to negative values of weight coefficientsbased on the Bessel function; and with respect to high-frequency ranges,speaker units are each driven with weighting using weight coefficientsbased on the Bessel function; hence, it is possible to avoid theoccurrence of beams and comb shapes in sound. Therefore, it is possibleto avoid the occurrence of beams and comb shapes in audio emissioncharacteristics in a broad range of frequencies ranging fromlow-frequency ranges to high-frequency ranges, and it is possible torealize efficient audio emission in which a sound field is formed in aspherical manner.

Incidentally, this invention is not necessarily limited to theaforementioned embodiments; hence, it may embrace design changes withinthe scope of the invention.

1. An array speaker system that is constituted by arraying a pluralityof speaker units, wherein all the speaker units are driven with a samephase with respect to low-frequency signals, and the speaker units areeach driven with weight coefficients based on a Bessel function withrespect to high-frequency signals.
 2. An array speaker system that isconstituted by arraying a plurality of speaker units, wherein all thespeaker units are driven with a same phase and with a same gain withrespect to low-frequency signals, and the speaker units are each drivenwith weight coefficients based on a Bessel function with respect tohigh-frequency signals.
 3. An array speaker system that is constitutedby array a plurality of speaker units, said array speaker systemcomprising an all-pass filter whose phase is subjected to rotation by180° in high-frequency ranges, wherein ones of the speaker units whoseweight coefficients based on a Bessel function have negative values areeach driven with weights corresponding to absolute values of the weightcoefficients, which are imparted to a signal transmitted through theall-pass filter, and wherein ones of the speaker units whose weightcoefficients based on the Bessel function do not have negative valuesare each driven with the weight coefficients thereof.
 4. An arrayspeaker system that is constituted by arraying a plurality of speakerunits, said array speaker system comprising: an all-pass filter whosephase is subjected to rotation by 180° in high-frequency ranges; a meansthat is provided in connection with each of ones of the speaker unitswhose weight coefficients based on a Bessel function have negativevalues and that inputs a signal transmitted through the all-pass filterso as to impart gain characteristics, corresponding to absolute valuesof the weight coefficients, to signal components of high-frequencyranges; and a means that is provided in connection with each of ones ofthe speaker units whose weight coefficients based on the Bessel functiondo not have negative values and that imparts gain characteristics,corresponding to the weight coefficients thereof, to signal componentsof high-frequency ranges.
 5. An array speaker system according to claim3, wherein the all-pass filter has a phase rotation that is set to 90°with respect to frequencies in proximity to a frequency matching awavelength corresponding to a width of each speaker unit within an arrayof the speaker units.
 6. (canceled)
 7. An array speaker system that isconstituted by arraying a plurality of speaker units, said array speakersystem comprising: a filter means for dividing an input signal intosignal components of low-frequency ranges and signal components ofhigh-frequency ranges; a weighting means that is provided in connectionwith each of the speaker units and that imparts weight coefficientsbased on a Bessel function to the signal components of thehigh-frequency ranges, which are divided by the filter means; and anaddition means that is provided in connection with each of the speakerunits and that adds the signal components of the low-frequency ranges,which are divided by the filter means, to the signal components of thehigh-frequency ranges, to which the weighting means imparts the weightcoefficients based on the Bessel function, thus outputting additionresults to the corresponding speaker units.
 8. An array speaker systemaccording to any one of claims 1 to 5 and 7, wherein the plurality ofspeaker units are installed in a common enclosure.
 9. An array speakersystem according to any one of claims 1 to 5 and 7, wherein theplurality of speaker units are installed in a common enclosure of abass-reflex type.
 10. A driving method for an array speaker system thatis constituted by arraying a plurality of speaker units, said drivingmethod for an array speaker system comprising the steps of: driving allthe speaker units with a same phase with respect to low-frequencysignals; and driving the speaker units separately with weightcoefficients based on Bessel function with respect to high-frequencysignals.
 11. A driving method for an array speaker system that isconstituted by arraying a plurality of speaker units, said drivingmethod for an array speaker system comprising the steps of: driving allthe speaker units with a same phase and with a same gain with respect tolow-frequency signals; and driving the speaker units separately withweight coefficients based on a Bessel function with respect tohigh-frequency signals.
 12. A driving method for an array speaker systemthat is constituted by arraying a plurality of speaker units and thatincludes an all-pass filter whose phase is subjected to rotation by 180°in high-frequency ranges, said driving method for an array speakersystem comprising the steps of: driving ones of the speaker units whoseweight coefficients based on a Bessel function have negative values withweights corresponding to absolute values of the weight coefficients,which are imparted to a signal transmitted through the all-pass filter;and driving ones of the speaker units whose weight coefficients based onthe Bessel function do not have negative values with the weightcoefficients thereof.
 13. A driving method for an array speaker systemthat is constituted by arraying a plurality of speaker units and thatincludes an all-pass filter whose phase is subjected to rotation by 180°in high-frequency ranges, said driving method for an array speakersystem comprising the steps of: inputting a signal transmitted throughthe all-pass filter so as to impart gain characteristics, correspondingto absolute values of weight coefficients, to signal components ofhigh-frequency ranges with respect to ones of the speaker units whoseweight coefficients based on a Bessel function have negative values; andimparting gain characteristics, corresponding to the weightcoefficients, to the signals of the high-frequency ranges with respectto ones of the speaker units whose weight coefficients based on theBessel function do not have negative values.
 14. The driving method foran array speaker system according to claim 13, wherein the all-passfilter has a phase rotation that is set to 90° in frequencies inproximity to a frequency matching a wavelength corresponding to a widthof each speaker unit within an array of the speaker units. 15.(canceled)
 16. A driving method for an array speaker system that isconstituted by arraying a plurality of speaker units, said drivingmethod for an array speaker unit comprising the steps of: dividing aninput signal into signal components of low-frequency ranges and signalcomponents of high-frequency ranges; imparting weight coefficients basedon a Bessel function to the signal components of the dividedhigh-frequency ranges with respect to the speaker units respectively;and adding the signal components of the divided low-frequency ranges tothe signal components of the high-frequency ranges, to which the weightcoefficients based on the Bessel function are imparted, thus outputtingaddition results to the speaker units respectively.